HP 3000 Manuals HP 3000 Manuals
Trap Handling [REV BEG] Traps occur when Transact encounters specific arithmetic errors, Pascal library errors, or a control-y is issued. When an arithmetic trap is discovered in a Transact program, an error is issued and processing stops. Transact does not always process traps in the same way depending on whether they occur in the main program, a called subprogram, an Inform system, or an ACI subprogram. The different types of processing for Transact trap handling are described below. Trap handling can also be modified by specifically calling the trap intrinsics via the PROC verb. System Initialization Arithmetic traps are armed and enabled during initialization of a Transact program. ARITRAP and XARITRAP are called to enable and arm the arithmetic traps. Control-y traps are also enabled during initialization by issuing the XCONTRAP intrinsic. For Transact/iX, the Pascal library traps are set by calling XLIBTRAP. PROC When calling a subprogram (other than a Transact subprogram) using the PROC call, you can select the TRAP or NOTRAP option. If no option is selected, the default TRAP option is used. When the TRAP option is used, any arithmetic or library traps that occur in the subprogram result in an error message. The subprogram terminates, and control is returned to the main program. If NOTRAP is specified in the PROC statement, all arithmetic traps are ignored in the subprogram, and processing continues as if no problems occurred. No status or information is passed back to the main program with either option. Online and batch modes are processed in the same way. CALL When calling a Transact subprogram, arithmetic traps and control-y are not disabled. Trap handling in the main program is the same throughout the Transact subprogram. In batch mode, the called subprogram issues an error message and terminates. Control is returned to the main program and processing continues. When calling an Inform or Report program, control-y is first disabled then re-enabled after the Inform or Report program completes. Arithmetic traps are not enabled or disabled. The arithmetic trap that is set at the time of the call is used throughout the Inform or Report program. ACI When the Architected Call Interface (ACI) intrinsic TL_CALL_TRANSACT is used to call a Transact subprogram from another language, the main program's arithmetic trap handling is saved, then re-enabled before returning to the main program. The Transact subprogram enables arithmetic and library traps during initialization. HPENBLTRAP is called to enable arithmetic traps, then XARITRAP is called to arm them. XLIBTRAP is called to arm the library traps. For more information about ACI see Appendix D. LET The LET verb has two modes for handling errors. The default mode is automatic, and occurs when the error message is displayed and processing continues to the next statement. The other mode, error branching, occurs when an error branch is specified in the LET statement. When certain errors are encountered, control is transferred to the error branch, and no error message is displayed. When the default mode is used in batch mode, an error on the LET verb will cause the program to terminate. For more information see the LET verb in Chapter 8. IF, REPEAT, WHILE When an arithmetic error occurs in the IF, REPEAT, or WHILE statements, an error message is displayed, and processing continues to the next statement. In batch mode, the error causes the program to stop. For more information see the IF, REPEAT, or WHILE statements in Chapter 8.[REV END]